Prince Philip, reportedly, made a shocking threat to Princess Diana decades ago.

In the book Diana: Her True Story, royal author Andrew Morton revealed that Princess Diana and Prince Philip exchanged bitter letters with each other.

The Duke of Edinburgh, reportedly, became convinced that Princess Diana gave her consent to release the book and expose Prince Charles’ affair. In his letter to the Princess of Wales, Prince Philip urged Princess Diana to help maintain the dignity of the crown.

Prince Philip also told his daughter-in-law to fit or get out. Otherwise, she would lose custody of Prince William and Prince Harry.

After reading Prince Philip’s letter, Princess Diana became enraged. She also, reportedly, declared that she’s out. Prince William and Prince Harry’s mom responded to Prince Philip by seemingly giving a suggestion that she would no longer stay married to Prince Charles.

After Prince Philip read the letter, he became more compassionate towards the late royal. And in Princess Diana’s words, she said that should’ve put her foot down years ago.

In 2018, The Sun published never before seen photos of Prince Philip and Princess Diana’s letter exchanges.

In 1992, Princess Diana wrote a letter to Prince Philip calling him “pa.”

“Thank you for responding to my letter so speedily – I agree that this form of communication does seem to be the only effective one in our present situation, but that it at least a start and I am grateful for it. You are very modest about your marriage guidance skills, and I disagree with you,” she wrote.

“Charles was silly to risk everything with Camilla for a man in his position. We never dreamed he might feel like leaving you for her. I cannot imagine anyone in their right mind leaving you for Camilla. Such a prospect never even entered our heads. I can only repeat what I’ve said before if invited, I will always do my utmost to help you and Charles to the best of my ability. But I am quite ready to concede that I have no talent as a marriage counselor,” Prince Philip replied.

However, the queen’s husband also told Princess Diana very early on that he wouldn’t support her having new romantic relationships. After all, he doesn’t also approve of Prince Charles having an affair, but they weren’t able to do anything about it.

In 1997, Princess Diana died in a car crash. And Prince Philip was one of the male royals that walked behind her coffin.